Hydraulically timed electrical switch



United States Patent Ofificc 3,035,521 Patented May 22, 1962 3,035,521 HYDRAULICALLY TIMED ELECTRICAL SWITCH George H. Hynard, Mundelein, Ill., assignor to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Filed June 30, 1955, Ser. No. 519,058 1 Claim. (Cl. 102-702) The invention relates generally to electrical switches and more particularly to a switch for closing or opening a circuit with a predetermined time delay following initiation of its actuation by the setback or centrifugal force of a projectile discharged from a gun, or by manual release, assuming a loaded compression spring as the driving medium.

More particularly the invention relates to an improved switch mechanism for arming the fuze, and hence the projectile, in response to the centrifugal force as the projectile is discharged from the rifle, or by the setback or inertia force resultant from the discharge of the projectile.

It is thus an object of the invention to provide an improved switch mechanism which is operated by centrifugal force, and the operation of which is timed by the flow of hydraulic fluid through an orifice.

A further object is to provide an improved hydraulically controlled switch mechanism which is adapted to be operated by centrifugal force and used in the projectile to delay the arming thereof.

Other objects Will appear from the following description, reference being had to the accompanying drawings in which FIG. 1 is an enlarged plan view;

FIG. 2 is a central vertical sectional view taken on the lines 2-2. of FIG. 1;

FIG. 3 is a diagrammatic base end view of a projectile showing the location of the switch therein; and

FIG. 4 is a schematic diagram of a circuit in which the centrifugally powered, hydraulically controlled switch may be incorporated.

Referring to FIGS. 1 and 2, the switch mechanism is housed in a generally cylindrical container 10, having an enlarged outer end portion 12 for reception of an insulating washer 14 comprising a layer 16 of synthetic, oilresistant rubber and a layer 18 of a fibrous phenolic composition.

The double-layered washer 14 is clamped in the outer end portion 12 of the base by a spun flange 20 forming part of the case. A three-fingered contactor 22 is secured to the double Washer 14 by a rivet 24. The rivet 24 also holds a soldering lug 26 in place, a washer 28 being provided to distribute the pressure and assure good contact between the lug and the rivet, as well as prevent oil leakage.

The fingers 22 are preferably made of a resilient, good electrical conductor such as beryllium-copper or Phosphor bronze. The fingers 22 are biased to move toward the axis of the casing and thus resiliently engage the hollow stem 30 of a piston 32 which is reciprocable within the casing 10 and which is biased to be held in its inner radial position (referring to FIG. 3), by a compression coil spring 34. The stem 30 of the piston 32 is provided with an extension 36 which has a cylindrical bore 38 therein. A metering cup 40, having an orifice 42 therein, fits closely within the bore 38 and is sealed by a suitable gasket 44.

The piston 32 has a sealing washer 46 which is secured in position by a clamping ring 48, the latter being secured by a press fit over a portion of the piston 32. The sealing member 46 is preferably made of Teflon or other suitable insulating material which is highly resistant to changes in characteristics due to contact with oil, which washer has a low coelficient of friction, and which has sufiicient elasticity to conform to the internal walls of the cylindrical casing 10 and which will maintain its elasticity and flexibility through a wide range of temperature.

A washer 50, having a soldering lug 52 formed integral therewith, is brazed or soldered to the casing 10. The casing 10 is completely filled with a hydraulic fluid such as a silicone oil which maintains its viscosity quite uniform throughout a substantial range of temperature.

The manner in which the switch heretofore described may be used is illustrated in FIGS. 3 and 4. In FIG. 3 the switch housing 10 is illustrated as being mounted radially within a projectile 60 which is adapted to be fired from a rifle, having riding to impart a gyro-rotational effect to the projectile.

Assuming FIG. 3 represents the outlines of the projectile 60, looking from the breech end of the rifle, the projectile will, upon explosion of its propelling charge, rotate clockwise.

Within the fuze mechanism of the projectile there may be provided a source of electrical energy 62, illustrated schematically in FIG. 4, which is normally short-circuited by the switch 22, 30. The circuit includes a resistance element 64 which may form part of a detonator or primer to initiate the detonation of the projectile. It will be apparent that the heating or energization of the resistor 64 is prevented while the switch 22, 30 is closed.

As the projectile is propelled from the rifle and the gyro-rotary twist imparted thereto, the mass of piston 32, due to centrifugal force, tends to force the hydraulic fluid from the radially outward chamber 70 to the chamber 72 through the orifice 42. The rate of the transfer of the hydraulic fluid from the chamber 70 to the chamber 72 may be accurately determined by the size of the orifice 42, taking into consideration the type and size of shell and kind of cannon or rifle which is to be used to fire the shell.

As the centrifugal force acting on the piston 32 causes transference from chamber 70 to chamber 72 of the hydraulic fluid, the resilient fingers 22 maintain contact with the piston stem 30 until shortly before the piston reaches the radially outward end wall of the housing 10. Upon opening the switch 22, 30 (FIG. 4), the full output of the electrical power source 62 is available to be impressed across the igniter resistance 64 to detonate the priming charge, causing explosion of the charge. In the majority of instances a suitable switch 66 will be provided, in series with the resistance igniter 64, which switch would be arranged to be closed upon impact.

By use of this hydraulically controlled switch in the particular combination disclosed, it will be assured that the shell will have advanced sur'ficiently from the muzzle of the rifle so as to protect the firing personnel from possible injury.

Inasmuch as the switch mechanism has three switch fingers resiliently engaging the piston stem 30, it will be clear that the possibility of failure to complete the circuit between the two soldering contacts 22 and 26, due to foreign particles, etc., is extremely unlikely. The fact that the switch contacts are provided with a plurality of fingers angularly spaced from one another, greatly minimizes the chance that the srm'tch might be opened as a result of impact irrespective of the direction of the inertia forces or momentum to which it may be subjected.

The orifice 42 is provided in the cup 40, as distinguished from being formed in the piston 32, so that merely by substituting cups 40 with diflerent sized orifices, the desired delay in the arming of the projectile may be predetermined.

It is particularly important that the seal 46 function very positively to prevent leakage from one side of the piston to the other, and it is for this reason that it is made of a material which, as previously stated, is highly suited for the purpose. The efiectiveness of the 'seal '46 is enhanced by the fact that it is of greater outside diameter than the internal diameter of the casing 10, and as a result its peripheral edge is flexed toward the direction from which the seal will be subjected to pressure. The seal thus acts in the manner of a cup washer. The pressure differential on the opposite sides of the seal operates to increase the eftectiveness of the seal.

Furthermore, it will be noted that the thickness of the metal of which the cup 40 is made is intentionally made very small. (The views of the switch in FIGS. 1 and 2 are approximately five times oversize). The reason for making the cup 40 out of thin sheet metal is to make it possible more accurately to control the rate of flow of the hydraulic fluid throughthe orifice 42, because the fiow rate will be determined substantially solely by the orifice resistance and will not be materially changed by pipe resistance. For example, in one embodiment of the invention the cup '40 was made of Phosphor bronze sheet metal having a thickness of approximately .004", the orifice 42 having a diameter ofapproximately .006. In the use of the switch mechanism, the compression spring 34 operates to resist radially outward movement of the piston 32 and serves the purpose of normally maintaining the piston 32 in the position shown in FIG. 2, so that if, for example, the shell were lying in a position such as that the force of gravity, plus possible vibration, would tend to move the piston radially outwardly, this possibility would be prevented by the spring 34. Moreover, if for some unknown reason the shell fails to detonate at impact, the spring 34 will apply a force to the piston 32 to cause it to return to a position in which its stem 30 is in electrical contact with the fingers 22, thereby shorting the resistor 64 (FIG. 4) and thereby rendering the projectile safe against accidental explosion.

While I have shown and described a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claim, to include within the scope of the invention all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

For use in arming a projectile in response to its rotation on its axis, a delay deviceadapted for mounting within the projectile in a position having a substantial component extending radially from the axis of the projectile comprising a casing having a cylindrical bore re- Iceiving a hydraulic fluid of the type having a substantially uniform viscosity throughout a substantial range of temperature, a piston reciprocably received in the bore, an elastic annular washer carried by the piston in sealing relation with the adjacent inner periphery of the bore to prevent appreciable leakage between the piston and casing bore, a spring urging the piston radially inward with respect to the longitudinal axis of the projectile, an element carried by the piston and having a thin, sharpedged measuring orifice of shorter length than its diameter for accurately controlling the rate of flow of the fluid from one side of the piston to the other as the piston moves radially outwardly to a predetermined position incident to gyro-rotary movement of the projectile as it is propelled from a rifle, a cylindrical boss extending axially from the piston, and a plurality of circumferentially spaced resilient electrical contacts secured to the casing and biased toward and slidably engaging the outer periphery of the boss to establish electrical continuity therewith, the contacts electrically disengaging the boss incident to movement of the piston to a predetermined Gascoine et al Sept. 25, 1956 

